1. Field of Use
This invention relates generally to material handling devices, and more particularly to traveling cranes supported by overhead rails and having a vertical, rigid telescoping mast on which a load carriage is vertically movable and capable of lifting and transporting a cylindrical load such as a metal coil. These devices are sometimes referred to as stacker cranes.
2. Description of Prior Art
Coil lifting and transporting devices of the type to which the present invention relates have overcome some of the problems associated with the art, but each has been deficient in at least one important respect.
Several devices have provided means for engaging a coil that are somewhat dangerous. Some prior art lifters engage a coil in its center aperture and also along its periphery with a pair of jaws. However, some of these lifters, such as those described in U.S. Pat. No. 3,104,016, issued to Harry, on Sept. 17, 1963, have relied upon hydraulic cylinders to maintain the jaws in tight wedging engagement with the coil. Malfunction of a hydraulic cylinder or loss of hydraulic fluid while the Harry lifter is moving an elevated load would create a potentially serious hazard. Other lifters, such as those described in U.S. Pat. No. 2,999,716, issued to Elberty, on Sept. 12, 1961 have the coil-engaging apparatus suspended from a cable, with a hook attaching the cable to the apparatus at a horizontally-disposed pin therein. The pin and hook create a pivot point about which the suspended apparatus and coil may swing in an uncontrollable fashion.
Other devices, including Elberty, have used a pad sliding on an inclined surface of a jaw to more tightly engage a coil between a pair of jaws. Such devices, however, require two sliding pads, one on each jaw, to engage a coil for lifting and further show that both the jaw engaging the coil at its center aperture and the jaw engaging the coil along its periphery be movable with respect to the gear quadrant which rotates the coil through a ninety degree arc. These features unnecessarily complicate such devices and add to their fabrication expense and potential for maintenance.
Other coil handling devices are lacking features which would give them broader utility. Among these are devices, such as that described in U.S. Pat. No. 2,630,931, issued to Douglas on Mar. 10, 1953, which engage the coil with magnets, disenabling them from handling aluminum coil. Still others, such as that described in U.S. Pat. No. 3,734,328, issued to Dalglish, on May 22, 1973, are not able to transport coils over obstructions on the floor, as there is no ground clearance between the bottoms of the fully raised devices or the coils carried thereby and the ground.